assistant2: Encourage diagnostics check (#27510)

Release Notes:

- N/A

crates/assistant_tool/src/assistant_tool.rs

@@ -80,6 +80,8 @@ pub struct ActionLog {
     stale_buffers_in_context: HashSet<Entity<Buffer>>,
     /// Buffers that we want to notify the model about when they change.
     tracked_buffers: HashMap<Entity<Buffer>, TrackedBuffer>,
+    /// Has the model edited a file since it last checked diagnostics?
+    edited_since_project_diagnostics_check: bool,
 }
 
 #[derive(Debug, Default)]
@@ -93,6 +95,7 @@ impl ActionLog {
         Self {
             stale_buffers_in_context: HashSet::default(),
             tracked_buffers: HashMap::default(),
+            edited_since_project_diagnostics_check: false,
         }
     }
 
@@ -110,6 +113,12 @@ impl ActionLog {
         }
 
         self.stale_buffers_in_context.extend(buffers);
+        self.edited_since_project_diagnostics_check = true;
+    }
+
+    /// Notifies a diagnostics check
+    pub fn checked_project_diagnostics(&mut self) {
+        self.edited_since_project_diagnostics_check = false;
     }
 
     /// Iterate over buffers changed since last read or edited by the model
@@ -120,6 +129,11 @@ impl ActionLog {
             .map(|(buffer, _)| buffer)
     }
 
+    /// Returns true if any files have been edited since the last project diagnostics check
+    pub fn has_edited_files_since_project_diagnostics_check(&self) -> bool {
+        self.edited_since_project_diagnostics_check
+    }
+
     /// Takes and returns the set of buffers pending refresh, clearing internal state.
     pub fn take_stale_buffers_in_context(&mut self) -> HashSet<Entity<Buffer>> {
         std::mem::take(&mut self.stale_buffers_in_context)